Eicosanoic

Part of speech: adjective

Definitions

1. Describing a fatty acid or other organic compound having a chain of twenty carbon atoms
2. Relating to or denoting a hydrocarbon structure composed of exactly twenty carbon atoms bonded together
3. Characterizing any organic molecule with a twenty-carbon skeleton, particularly in reference to saturated fatty acids

Etymology: Eicosanoic is a chemistry term built in the lab rather than handed down through speech. It is formed from "eicosane," the name for a straight-chain alkane with twenty carbon atoms, with the suffix "-oic" added to mark a carboxylic acid. The two parts map cleanly onto the chemistry: the "eico-" element is the Greek numeral for twenty, so the stem points to the twenty-carbon chain, and the "-oic" ending signals the acid group at its end. The name thus describes the molecule's structure in a single word. Eicosanoic acid is the saturated fatty acid with twenty carbons, also known as arachidic acid, and the systematic name tells a chemist its length and functional group without any further explanation. The pattern is shared with other systematic names such as "octanoic" for the eight-carbon acid, so anyone who knows the numerical stems can work out the meaning of an unfamiliar acid name.